Prior hammer drill chucks generally comprised of a chuck body connected to a drive shaft of a drilling machine which provides hammer blows to a drill tool, a mounting opening in the chuck body for mounting the drill bit shaft coaxially with the chuck axis, a plurality of clamp jaws guided in the chuck body advanceable to and retractable from the mounting opening centrally and preferably inclined downwardly toward the drill bit, and an axial passage in the chuck body between the drive shaft and the mounting opening, through which the hammer blows are transmitted directly onto the end of the drill bit shaft in the mounting opening.
The hammer blows may be transmitted directly to the drill bit shaft by the axially mounted drive shaft which moves axially with respect to the chuck. Nevertheless it is also possible to provide a hollow drive shaft in which there is an axial passage therethrough down through which a ram moves axially to deliver hammer blows to the drill bit shaft.
In these prior art chucks it is a disadvantage in that the drill bit shaft in the clamp jaws shortly after operation is begun loosens to the extent that the drill bit can follow the hammer blow motion relative to the fixed clamp jaws. This loosening of the drill bit in the clamp jaws and the relative axial displacement of drill bit and jaws, causes an increased wear not only on the drill bit shaft, but also on the clamp surfaces or the clamp jaw edges of the clamp jaws. The replacement of clamp jaws made unserviceable by wear requires an increased expense and specially trained personnel.